Molecular Separators, Concentrators, and Detectors Preparatory to Sensor Operation, and Methods of Minimizing False Positives in Sensor Operations

ABSTRACT

As an elegant solution for minimizing false positives returned by a sensor tuned to an analyte molecule, filters constructed of carbon nanotubes are positioned relative to the sensor to limit the sensor to being exposed to molecules within a defined range of sizes, with too-big molecules being excluded from reaching the sensor by one filter, and too-small molecules being pumped out through another, finer filter before the sensor is operated.

RELATED APPLICATION

This application claims benefit of U.S. provisional application Ser. No.61/111,048 filed Nov. 4, 2008, the contents of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to detection of molecules,especially detection of molecules such as chemical warfare agents, whilereducing or avoiding false alarms.

BACKGROUND OF THE INVENTION

The sensing of analytes (such as chemical warfare agents, etc.) withconsiderable sensitivity and specificity is a requirement in manycircumstances. Sensitivity is required to sense analytes before theirlevel reaches an undesired value. Specificity is necessary to avoidfalse positives that would engender unnecessary, costly, and potentiallydangerous responses.

Chemical warfare agents are lethal compounds applied to warfare havebeen developed over many years, some derived from commercial compoundsused to control destructive animals, insects, and plants, others aretoxic industrial chemicals, such as chlorine, that also have been usedin warfare. Still others are the product of military research anddevelopment intended to produce lethal agents of desired characteristicsand effects.

The complexity and variety of chemical compounds, many only slightlydifferent in structure or chemical reactivity, make the taskchallenging. False positive such as may originate from similar compoundspresent in the sampled environment are a source of concern.

For detecting certain molecules (such as chemical warfare agents, etc.),there are various conventional sensors and detectors that have beenpreviously provided. However, these existing sensors and detectors arenot without flaws and shortcomings. For one, there is wanted greatersensitivity, namely, the ability to detect on the order of parts pertrillion (ppt).

Significantly, current sensors and detectors tend to have a false alarm(false positive) problem, namely, that the sensors and detectors aretriggered not just by what is wanted to be detected but also triggeredby “interferents.” For example, in the case of current sensors used bythe chemical agent detector community, benzene and toluene are potentialinterferents. These chemicals are components of JP-8 and diesel fuelvapors and exhaust and associated with a variety of burning materialsand gunfire. False alarm problems have been reported in the testing ofcurrently used fieldable chemical agent detectors in the presence ofJP-8 and diesel vapor and exhaust, as well as toluene. In these tests apositive detection of either nerve or blister agents was registered whenneither of these chemical warfare agents was present.

Another example where sensitivity and specificity are needed is insensing compounds in the environment that are destructive to theatmosphere and water and endanger the health of those exposed. In othercases chemical sensing is important for the collection of informationabout criminal and foreign military developments and operations. Inindustrial operations, chemical sensing is necessary to recognize whendangerous processes may be incompletely contained, becominguncontrolled, and/or potentially creating a HAZMAT release.

There have not yet been provided, but are wanted, fieldable devices withsensors that are both sufficiently sensitive and versatile to providefor detection of a variety of important threat agents and simultaneouslydiscriminating of, or insensitive to, interferents which would registerfalse positives.

Also, there are needs for detecting toxic materials in water samples.The safety of drinking water is of importance for military deploymentsin combat zones. Domestically there is the treat of terrorist attacksagainst water supply systems. A large concern is the protection ofpopulations against toxic chemicals that find their way into drinkingwater, and into lakes, rivers, bays and oceans where they harm animalsand fish, and damage recreational uses of such natural resources.

SUMMARY OF THE INVENTION

The present inventor has provided an elegant solution to the difficultproblem of how to minimize false positive readings in a sensor,preferably while detecting the analyte or target molecules (such as,e.g., chemical warfare agent, etc.) at the desired sensitivity. Theinvention provides for preprocessing (such as, e.g., inventive molecularseparation) to be performed on a sample to sort molecules from thesample before a sensor (such as, e.g., a carbon nanotube bundle sensor)is operated on what remains of the sample.

The operation of an inventive molecular separator advantageously allowsthe molecular separator to function simultaneously as a concentrator bydrawing the sample through the invention as a continuous flow, at eachinstant trapping the desired molecules. This allows the analyte oranalytes thereby selected to accumulate in ever increasing numbers to adegree proportional to the amount of time the sample flow is maintained.Thus a variety of different sensors can be employed, varying in theirspecific characteristics, and regardless of limits on the minimumconcentration of analyte needed for them to produce a measurableelectrical or other signal relatable to the concentration of theintended analyte.

An objective of the present invention is to provide a physicaldiscriminant to reduce false positives, that of molecular size. In somecases, such providing of a physical discriminant may suffice to selectonly the desired compound from among the many possibly present andexposed to a chemical sensor. In other cases, additional a priorireasoning may be further performed to reduce or eliminate potentialinterfering compounds (also known as “interferents”) based on externalcircumstances of the site where the measurement is being made and otherinformation available remotely. In this invention, preferably a chemicalsensor is embedded in, and is a part of, a system created for somelarger purpose. In a significant class of applications, site-specificinformation can be drawn upon to manage the sensor and interpret thesensor's results.

The present invention recognizes and makes use of the fact that thesizes of molecules of concern in many sensing applications bear a closerelationship to the sizes of atomic-level nanostructures such as, e.g.,those of carbon nanotubes. Regularly-spaced columnar nanostructures canserve as molecular size filters for external flows.

The invention in one aspect provides a method of sorting molecules bysize, comprising: contacting at least one nanotube having an innerdiameter within a first predetermined diameter range, with an initialsample (such as, e.g., an initial sample that is a gaseous sample; aninitial sample of air; etc.) of various-sized molecules, to produce ascreened sample; such as, e.g., inventive methods further comprisingcontacting at least one nanotube of an inner diameter within a secondpredetermined diameter range which is not equal to the firstpredetermined diameter range, to a screened sample to produce asize-sorted sample (such as, e.g., inventive methods wherein the atleast one nanotube is contained within a first screen comprising aplurality of nanotubes having the first predetermined diameter range,and the at least one nanotube having the second diameter is containedwithin a second screen comprising a plurality of nanotubes having thesecond predetermined diameter range).

In another aspect, the invention provides a method of reducing aninitial sample (such as, e.g., an initial sample that is a gaseoussample) that contains various-sized molecules to a subset of moleculesof a predefined size range, comprising: screening the initial sample toproduce a screened sample consisting of molecules of size smaller than amaximum size (such as, e.g., a size D(max)); and requiring molecules ofsize smaller than a minimum size (such as, e.g., a size D(min)) to exit,such as, e.g., inventive methods comprising producing a target sampleconsisting of molecules having a size in a range of D(min) to D(max);inventive methods wherein the step of screening the initial sample toproduce a screened sample consisting of molecules of size smaller thanthe maximum size (such as, e.g., D(max)) includes applying a screencomprising at least one nanotube having an inner diameter to excludemolecules bigger than the maximum size; inventive methods wherein thestep of requiring molecules of size greater than the minimum size (suchas, e.g., D(min)) to exit includes applying a screen comprising at leastone nanotube having an inner diameter that permits passage of moleculesbelow the minimum size (such as, e.g., D(min)); inventive methodscomprising passing the initial sample through a screen comprising atleast one nanotube having an inner diameter to exclude molecules biggerthan the maximum size, followed by withdrawing, through a screencomprising at least one nanotube having an inner diameter that permitspassage of molecules below the minimum size (such as, e.g., D(min)), asubset of molecules which are smaller than the minimum size (such as,e.g., D(min)), such as, e.g. inventive methods comprising performing thewithdrawing step until the initial sample has been transformed into atarget sample consisting only of molecules of the predefined size range;inventive methods comprising screening an initial sample that is agaseous sample; inventive methods comprising a screening step ofscreening an initial sample comprising at least one of an analytemolecule and/or a molecule that evokes a false positive for the analytemolecule; inventive methods comprising a screening step of screening aninitial sample comprising at least one pair of an analyte moleculeand/or a molecule that evokes a false positive for the analyte moleculeand is of a different size than the analyte molecule; inventive methodspracticed with a selective screening structure that comprises: a firstscreen comprising at least one nanotube having a first diameter; asecond screen comprising at least one nanotube having a second diameterwhich is smaller than the first diameter, wherein the selectivescreening structure has a size selectivity in a range between a minimumwhich equals about the second diameter and a maximum which equals aboutthe first diameter; and other inventive methods.

The invention in another aspect provides a method, comprising: for aninitial sample (such as, e.g., an initial sample that is a gaseoussample; an initial sample that includes at least one of an analytemolecule and/or a molecule that evokes a false positive for the analytemolecule; etc.) that contains various-sized molecules, reducing theinitial sample to a subset of molecules of a predefined size range (suchas, e.g., a reducing step that sorts from the initial sample moleculeswhich are outside of a size range), and bringing the subset of moleculesof the predefined size range into contact with at least one sensor (suchas, e.g., a carbon nanotube bundle sensor; a sensor configured to detecta chemical warfare agent; etc.), such as, e.g., inventive methodswherein the initial sample includes at least one of an analyte moleculeand/or a molecule that evokes a false positive for the analyte molecule;inventive methods wherein the initial sample includes at least one of ananalyte molecule and/or a molecule that evokes a false positive for theanalyte molecule, and the reducing step sorts the molecule that evokes afalse positive; inventive methods wherein the initial sample includes aset of molecules that are of a relatively large size, a set of moleculesthat are of a relatively small size, and a target set of molecules thatare of a medium size which is the predefined size range, and thereducing step reduces the initial sample to the target set; inventivemethods wherein the reducing step comprises a step of screening-outtoo-big molecules and further comprises a step of requiring too-smallmolecules to exit while screening-in target-size molecules; inventivemethods wherein the reducing step sorts at least one molecule that wouldevoke a false positive and prevents the molecule that would evoke thefalse positive from coming in contact with the sensor; and otherinventive methods.

In another aspect, the invention provides a method of sorting, from aninitial sample (such as, e.g., an initial sample that is a gaseoussample), a subset of molecules that would activate false positives by asensor which is intended to detect a molecule or molecules, comprising:for the sensor, identifying a size range of the analyte molecule ormolecules; sorting, from the initial sample, molecules outside theidentified size range of the analyte molecule or molecules (such as,e.g., a sorting step that comprises sorting molecules sized outside thesize range of the molecules intended to be sensed, before the sensor isapplied; a sorting step that comprises applying at least a first screencomprising at least one nanotube of an inner diameter that excludestoo-big molecules, and further comprises requiring too-small moleculesto exit through at least one nanotube of an inner diameter that permitspassage of too-small molecules; and other sorting steps), such as, e.g.,inventive methods wherein applying the first screen includes applying afirst screen that comprises an array of nanotubes of an inner diameterthat excludes too-big molecules, and wherein requiring too-smallmolecules to exit includes requiring too-small molecules to exit througha second screen that comprises an array of nanotubes of an innerdiameter that permits passage of too-small molecules; inventive methodswherein the requiring too-small molecules to exit includes operating apump to create a flow of sample; and other inventive methods.

For example, in an inventive method, when the class of molecules to besensed is that of nerve gases, the two filter sizes would be such thatmolecules smaller than 1.320 nm are allowed to enter theconcentrator/sensor cell and molecules smaller than 0.727 nm are allowedto exit from the concentrator/sensor cell (with these mentioned sizescorresponding, respectively, to the smallest and largest sizes of nerveagents, GB (sarin) at the small end of the selected range and the nerveagent VX at the large end of the size range).

The invention in another aspect provides a method of processing aninitial sample (such as, e.g., an initial sample that is a gaseoussample; an initial sample of air; etc.) of a set of molecules beforecontact with a sensor, comprising: directing the initial sample of theset molecules into contact with an entry screen leading into acontainer, the entry screen excluding from entry a subset of moleculesbigger than a molecular size range of molecules wanted to be detected bythe sensor; withdrawing from the container a subset of molecules smallerthan the molecular size range of molecules wanted to be detected by thesensor; such as, e.g., inventive methods further comprising operatingthe sensor in the container after the directing and withdrawing steps;inventive methods wherein the initial sample includes at least onemolecule that would evoke a false-positive and after the directing stepand the withdrawing step, the molecule that would evoke a false-positiveis not within the container; inventive methods wherein the initialsample includes at least one molecule that would evoke a false-positiveand at least one molecule that is intended to be detected by the sensor,and after the directing step and the withdrawing step, the molecule thatwould evoke a false-positive is not within the container and themolecule that is intended to be detected by the sensor is within thecontainer; and other inventive methods.

In another aspect the invention provides a molecular separatorcomprising: a chamber comprising at least a first screen and a secondscreen; the first screen comprising at least one nanotube having aninner diameter that is a first diameter or within a first range ofdiameters; the second screen comprising at least one nanotube having aninner diameter that is a second diameter or within a second range ofdiameters, which is smaller than the first diameter or first range ofdiameters, such as, e.g., inventive molecular separators furthercomprising: an inlet valve upstream of the chamber, a pump downstream ofthe chamber and an exit portal through which molecules beingseparated-out as too small exit the chamber; inventive molecularseparators further comprising a sensor (such as, e.g., a carbon nanotubebundle sensor) disposed within or inserted into the chamber.

The invention in a further aspect provides a molecular separator whichseparates molecules of a class defined by a specified physicalcharacteristic, such as, e.g., inventive molecular separators thatseparate molecules that are in a gaseous medium; inventive molecularseparators that separate molecules while distinguishing betweenmolecules of other classes having similar physical characteristics;inventive molecular separators that distinguish between molecules havinga specified parameter greater than a D(min) and less than a D(max);inventive molecular separators that include a sensor to produce aquantitative measure of the concentration of the defined class ofmolecules in the range of 1 ppm (part per million) to 1 ppt (part pertrillion); inventive molecular separators that can be used in both urbanand rural locations; inventive molecular separators that separatemolecules in a time period of less than 5 minutes; man-portableinventive molecular separators; inventive molecular separators that canbe used in an automated or semi-automated mode of operation; and otherinventive molecular separators.

In another aspect the invention provides a method of nanotube screening,comprising: vaporizing to convert analytes that may be present in thesample as liquid phase droplets to reduce such droplets to a vaporphase, and nanotube screening after vaporizing.

The invention in another aspect provides a method of assessing whether asensor which has returned a positive indication is false-alarming,comprising: when the sensor has returned the positive indication forpresence of a target substance, operating a software-based querysequence in which a series of yes/no queries are presented to a humanuser for yes/no response, wherein each yes/no query tends to screen forwhether the target substance is actually present and being detected bythe sensor or whether instead the sensor could issue a false alarm.

In a further aspect the invention provides an interactive interrogatorsystem for detecting a target substance, comprising: a sensor tuned todetect the target substance; and a computer-based interrogator systemthat is interactive with a user and that provides a series ofinteractive queries that when answered by the user tend to screen forwhether the sensor is indeed detecting the target substance or could bedetecting a non-target substance that would cause a false alarm.

In another aspect, the invention provides a sensor-based method ofdetecting an analyte (such as, e.g., tabun, soman, cyclosarin, etc.),such as, e.g., inventive detecting methods that comprise a step ofsubjecting an initial sample to a length separation operation (such as,e.g., a subjecting to a length separation step that sorts the initialsample into a size-sorted sample including a mid-sized sample) inadvance of a step of operating the sensor (such as a sensor for ananalyte) to take a measurement (such as, e.g., a step of operating thesensor to take a measurement of the mid-sized sample), followed by anambiguity-resolving step (such as, e.g., an ambiguity-resolving stepperformed with respect to the mid-sized sample for which the measurementwas taken in the step of operating the sensor); and other inventivesensor-based detecting methods that reduce false alarms to a low level.

In another aspect, the invention provides for detecting toxic materialsin water samples.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic showing a detector conceptaccording to an embodiment of the invention in which the inventivescreens (≡) are particularly noted.

FIG. 1A shows a cross-sectional schematic view of a nanotube which is apreferred component of a screen in FIG. 1, with a molecule small enoughto pass through the nanotube also shown. As a general state of affairs,analytes will be elongated rather than spherical, as shown hereschematically. However as a result of their rapid kinetic motion andtheir frequent collisions with one another and with the containingwalls, they have both translational and rotational kinetic energy. Thusan analyte, though it has an elongated shape, is treated as aminimum-size circumscribing sphere for addressing the relative size ofan analyte and a nanotube through which it travels.

FIG. 2 is a part of a table which may be used in practicing theinvention in an embodiment where a target molecule is tabun, somanand/or cyclosarin; other than the rows for tabun, soman and cyclosarinwhich are nerve agents, the two left-most columns in FIG. 2 indicateinterferents. In FIG. 2, the data for the nerve agents and interferentsinclude a standard chemical identification number, molecular weight,melting point, boiling point, vapor pressure, chemical formula, and themaximum diameter. In FIG. 2, the rows have been sorted by maximumdiameter and are shown in increasing order of the diameter of a minimumcircumscribing sphere.

FIG. 3 is a block diagram that shows components used in constructing asystem 300 which is an inventive embodiment including at least one cell33.

FIG. 3A is a cross-sectional schematic of a cell 33 useable in system300 (FIG. 3). In FIG. 3A, numbering from FIG. 1 is repeated whereapplicable.

FIG. 4 is a diagram of an inventive system 300 corresponding to FIG. 3.

FIG. 5 is a flow chart for an inventive embodiment which includes anambiguity-resolving step 502.

FIG. 6 is a flow chart for an inventive reduced false-alarm,sensor-based method of detecting an analyte which comprises a step 601of subjecting an initial sample to length separation; a step 602 ofoperating a sensor to take a measurement; and an ambiguity-resolvingstep 603.

FIG. 7 is a diagram for an inventive embodiment in which water samplesare processed.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The invention may be appreciated with reference to the figures, withoutthe invention being limited thereto. Referring to FIGS. 1-1A, a detectorconcept may be appreciated, according to which may be constructed asystem 100 useful for detecting an analyte molecule (such as, e.g., ananalyte molecule which is a chemical warfare agent; etc.). “Analyte” isused herein according to its ordinary meaning in the chemical arts andrefers to a substance or chemical constituent which is the subject of ananalysis. An analyte substance might also in the literature be called atarget substance.

The system 100 includes a sensor 1 which can detect the analytemolecule, such as, e.g., a carbon nanotube (CNT) sensor. As someexamples for use as sensor 1, sensors useable as sensor 1 are known andcommercially available, such as, e.g., a sensor having electricalproperties that change with exposure to an analyte. However, before thisinvention, the state of the art for fieldable devices had not yetprovided sensors both sufficiently sensitive and versatile to detect avariety of important threat agents and simultaneously discriminate or beinsensitive to interferents which could register an excessive number offalse alarms, which problem system 100 addresses, improving thespecificity of a conventional sensor when used as sensor 1 within system100 compared to stand-alone use of the same sensor.

In system 100, the sensor 1 is disposed within a chamber 2. According tothe invention, in system 100, the chamber 2 housing the sensor 1 isdivided into an upstream section 21, a section 22 near the sensor 1, anda downstream section 23. Particularly, the system 100 is constructed tobe sensitive to an analyte molecule size, such as, e.g., considering thelength of the analyte molecule. For example, if the analyte molecule isa nerve gas, nerve gases are in the length range of 0.727 to 1.320 nm,the chamber 2 is divided to take into account that the analyte moleculeis in a length range of 0.727 to 1.320 nm. The system 100 is tuned (suchas, e.g., maximum length dimension-wise) to analyte molecule size byproviding a screen 10 that excludes all molecules bigger than the size(such as, e.g., length) of the analyte molecule, and by providing ascreen 11 that permits to pass all molecules smaller than the size ofthe analyte molecule. For example, if system 100 is being constructedfor an analyte molecule that is a nerve gas, the screen 10 is a screenthat excludes all molecules with length greater than 1.320 nm and thescreen 11 is a screen that permits passage of all molecules with lengthless than 0.727 nm.

Referring to FIG. 1, an initial sample is introduced via inlet 3 intothe system 100, and molecules smaller than the analyte molecule maketheir way to downstream section 23, while molecules bigger than theanalyte molecule remain in upstream region 21. Only molecules in thesize range of the analyte molecule accumulate in region 22 near thesensor 1. In the case of an analyte molecule which is a nerve gas whichis a range of about 0.727 to 1.320 nm, a system 100 is constructed foruse in a method in which the system 100 performs a reducing step thatsorts from an initial sample introduced via inlet 3 into the system 100molecules which are outside of a range of about 0.727 to 1.320 nm,requires molecules which are bigger than 1.320 nm to remain in theupstream region 21, and only permits molecules which are in the range of0.0727 to 1.320 nm to accumulate in the region 22 near the sensor 1.

In system 100, for screens 10, 11, screens comprising carbon nanotubesare preferred with screen 10 and screen 11 each being constructed withrespective dimensions. FIG. 1A shows a cross-sectional view of ananotube being used in screen 10. Each carbon nanotube used in thescreen 10 has a wall thickness, such as wall thickness 10 t is 0.26 nmwhich is the diameter of a carbon atom. The outer radius 10R of thecarbon nanotube in screen 10 is shown. For practicing the invention, theinner diameter of a nanotube is used. The inner diameter of a nanotubeis the outer diameter (such as twice the outer radius 10R) minus thewall thickness (such as 10 t), with some small adjustment made to reducethe effect of van der Waal's forces or interactions that might impedethe motion of the sampled molecules through the nanotube filter. Anexample of such a small adjustment is, e.g., to increase the effectivesize of the analyte to be sensed, and which is used in the selection ofthe inner diameter of the carbon nanotube filters, by an amountsufficient to reduce the likelihood of wall interactions impeding themovement of the analyte molecules in the sample.

When a nanotube is being used within a screen that excludes molecules ofa maximum size, the nanotube should have an inner diameter to excludemolecules bigger than the maximum size. When a nanotube is being usedwithin a screen that permits passage of molecules of a minimum size, thenanotube should have an inner diameter that permits passage of moleculesbelow the minimum size. It will be appreciated that the inner diameterof a nanotube being used within a screen 10 or a screen 11 is notnecessarily set exactly equal to the molecule size which is to beexcluded or permitted passage, respectively. The precise requirementsare established by increasing the effective size of the analyte to besensed, and which is used in the selection of the inner diameter of thecarbon nanotube filters, by an amount sufficient to reduce thelikelihood of wall interactions impeding the movement of the analytemolecules in the sample.

Much experimental evidence exists that molecules can easily pass axiallythrough nanotube structures when the molecule is smaller than theinternal diameter of the nanotube.

For example, one can be certain that a molecule that is 1.05 nm indiameter will not find its way easily through a carbon nanotube that isexactly 1.05 nm in inner diameter; therefore, if passage of moleculesthat are 1.05 nm in diameter is wanted, then an inner diameter of thenanotube through which the 1.05 nm diameter molecules are to pass shouldbe slightly larger than 1.05 nm diameter being an example whenconstructing a screen to be used to permit passage of molecules by anamount indicated above.

Screens 10, 11 (FIG. 1) preferably comprise more than one nanotube. Itwill be appreciated that within one screen, all nanotubes are notrequired to be of absolutely identical inner diameter; a range of innerdiameters is permissible for nanotubes within one screen as long as theydo not admit or pass molecules that would engender excessive falsealarms.

A screen 10, 11 optionally may comprise a compound filter that comprisestwo or more carbon nanotube arrays in series, such as two carbonnanotube arrays in series comprising a first carbon nanotube array whichdiffers from a second nanotube array as to respective size screening. Acompound filter may be used to sharpen size sorting capability of ascreen 10 or a screen 11.

An example for constructing system 100 is to use macro size technologyfor the sensor 1, MEMS technology for the chamber 2, and nanotechnologyfor the screens or filters 10, 11.

The inventive system 100 of FIG. 1 advantageously may be used forsensing analyte molecules using the sensor 1 while excluding interferentmolecules from being sensed by the sensor 1, of a size suited to thesizes of nanotube filters that can be constructed.

The present invention provides an elegant solution addressing theproblem of false positives returned by a sensor configured for ananalyte (such as, e.g., sensor 1 in FIG. 1), such as, e.g., inventivepositioning of screens or filters (such as, e.g., filters constructed ofcarbon nanotubes) relative to the sensor 1 to limit the sensor 1 tobeing exposed to molecules within a defined range of sizes, withmolecules bigger than the defined range being excluded from reaching thesensor by one filter 10, and with molecules smaller than the definedrange being caused to exit (such as, e.g., pumped) through another,finer filter 11 before the sensor 1 is operated.

The system 100 (FIG. 1) may be used, e.g., for sorting different-sizedmolecules into three size categories including relatively-big molecules,molecules of target-size (such as, e.g., molecules of a size of nervegases), and relatively-small molecules.

Referring to system 100, in which too-big molecules accumulate inupstream section 21 and analyte molecules accumulate near the sensor 1,after the sensor 1 has been applied to make a measurement, if the system100 is to be re-used on a new initial sample, first the system 100should be evacuated such as by back-flushing.

In using an inventive system 100 (FIG. 1), the likelihood that thesensor 1 is sensing an interferent rather than the analyte molecule willbe greatly reduced compared to using a stand-alone sensor such as thesensor being used as sensor 1. However, in some cases, there will stillexist the possibility, albeit reduced, of a false positive, i.e., thatthe sensor 1 in system 100 is responding to presence of an interferentrather than presence of an analyte molecule. Approaches for resolvingwhether an interferent is present include, e.g., an assessment of theenvironment in which the system 100 is operating (such as, e.g., avisual determination by a human user that the sources of the interferentare not present); an ambiguity resolver which is a second sensordependent on a different physical parameter. The computer-basedambiguity resolver is preferred.

For example, in the course of operating an inventive sensor-based system(such as, e.g., system 100, system 300 (FIGS. 3-4), etc.), a response ofa sensor (such as, e.g., sensor 1 (FIG. 1), sensor S (FIGS. 3-4), etc.)is obtained through a step 500 (FIG. 5). In many cases necessarily thereis ambiguity whether the sensor response has been activated by ananalyte or, rather, by an interferent. Therefore, preferably the step500 of obtaining the sensor response is followed by anambiguity-resolving step 502 (such as, e.g., an ambiguity-resolving stepwhich comprises a visual assessment of the environment in which thesensor is operating; an ambiguity-resolving step which comprisesoperating a computer-based system; an ambiguity-resolving step includingobservations by a human user and prompting by a computer-based system;an ambiguity-resolving step which includes querying by a computer-basedsystem having stored therein a library (such as, e.g., a library ofcomputer-readable data relating to analytes and interferents) whereinthe computer-based system wherein the computer-based system queries atleast one human user and receives input from the human user; etc.

When the inventive system 100 (FIG. 1) is used to sort molecules in aninitial sample into too-big molecules, molecules of target size, andtoo-small molecules, optionally, sorted molecules of target-size may besubjected to further processing such as at least one further chamber(not shown in FIG. 1) that is specifically configured (such as throughat least one additional sensor which is different from sensor 1) tomeasure whether an interferent is present or interferents are present.

The invention may also be used, e.g., in environmental applications,first responder applications, hazardous materials applications, chemicalintelligence, law enforcement, etc.

The invention also may be applied to detecting and measuring theconcentration of toxic chemicals in water, such as, e.g., by inventivesystems and methods according to FIG. 7 (which is further discussed inInventive Example 5 below). Such an application to water samplesrequires, in addition to adequate sensitivity, chemical sensors thatoperate in water. The principles of the invention as described forworking with air samples are adapted with minor modification to the caseof water samples. The separator and concentration steps work as wellwith water as air. In addition to seeing large toxic molecules, thelength separators see, instead of a large number of molecules ofnitrogen, oxygen, carbon dioxide, and other atmospheric components, anequivalently large number of water molecules. In the case of applyingthe invention in water, the water flow is arranged so that after theselector/concentrator cells have collected enhanced levels of analytesof interest, the water is flushed out and replaced with air. Thusinstead of an integrated separator/concentrator cell having the chemicalsensor inside (as shown in FIG. 1), the sensor is in a separate cellthat always remains dry. Thus the modification consists of establishing“plumbing” for two separate fluid flow paths. One is wet and sees waterand analytes. The second is dry and sees air and the concentratedanalytes. Additional valves are used. In this application, the issue nowis not false positives triggering unnecessary defensive responses butrather the identification of the potentially wide range of toxicchemicals present. Time is no longer an issue because the water flowsare continuous and no immediate responsive action is required. Generallythe detector in this application does not have the severe limits onsize, weight, power, and speed that tactical warning or intelligencecollection missions impose. A second sensor, such as a mass spectrometeror other sensor, may be used for ambiguity resolution.

The invention may be appreciated with reference to the followingexamples, without the invention being limited thereto.

Inventive Example 1 Detector Concept

By “sensor” herein we mean a device placed in a concentration cell, suchas a sensor which is a nanotube sensor. We do not use the words “sensor”and “detector” interchangeably.

Referring to the accompanying FIGS. 1-1A, in system 100 a valve V11 atthe entry point is opened so that an entryway which is upstream region21 may receive the initial sample (which in this example is a gaseoussample, such as a sample of air of unknown composition). What ultimatelyis wanted is for the sensor 1 (such as a carbon nanotube (CNT) bundlesensor) to perform its actual sensing as would be done conventionally,but without being burdened by encountering molecules which give falsepositives and are not themselves wanted to be detected. However, at thesame time, it is wanted, e.g., for the sensor 1 to be able to detect ifan analyte molecule is present, even if present on the order of onlyparts per billion or trillion.

In this inventive example, the analyte molecules are considered and asize range is established for the analyte molecules. The inventivepreprocessing is to sort too-big molecules and too-small molecules fromthe initial sample and only present molecules in a size range for theanalyte molecules to the sensor 1. Referring to the figure, the initialsample encounters a first screen 10 (the left-most screen), said firstscreen 10 blocking entrance into a chamber 22 in which the sensor 1 isdisposed for operation in due time. Preferably, the first screen 10comprises a plurality of nanotubes each of a diameter to prohibitpassage of too-big molecules. For example, in the case where nerve gasesare the analyte molecules for the sensor, the first screen excludesmolecules with length greater than 1.32 nm.

Preferably a further preprocessing is performed, by applying a secondscreen 11 as shown in FIG. 1 (the right-most screen), which is a screenthrough which too-small molecules may pass but through which moleculeswithin the size range established for analyte molecules cannot pass. Forexample, in the case of nerve gases, the screen 11 for permitting exitof too-small molecules would molecules with length less than 0.927 nm toexit the chamber 22 in which the sensor 1 is disposed. For example,methane which is about 0.3 nm would exit. Preferably there is provided avalve V12 and a pump P downstream of the screen 11 that permitstoo-small molecules to exit, and the valve V12 is opened and the pump Pis operated to urge or require too-small molecules to exit the chamber22 in which is disposed the sensor 1.

For practicing the invention, it is preferable that the range of sizesof analyte molecules to be sensed by a single sensor 1 be in arelatively narrow range, that is, that the analyte molecules to besensed by sensor 1 are relatively close in size. For example, tabun,soman and cyclosarin which are nerve agents are relatively close insize, and a single inventive system 100 comprising sensor 1 sensingtabun, soman and cyclosarin as analyte molecules may be constructed.

Inventive Example 1A

Likewise to the manner that a molecular separator structure was providedin Inventive Example 1 configured for screening-out non-nerve gasmolecules for use with a nerve gas sensor, it readily can be appreciatedthat other respective molecular separator structures likewise can bemade with each molecular separator structure configured for its ownagent.

Preferably, the respective molecular separator structures each tuned toa respective analyte molecule are placed in parallel.

Inventive Example 1B Packaging Various Collections of Functionalities toAccommodate Different Domains of Applicability and User Requirements

1. Multiple size ranges or continuous spectrum of size measurement

-   -   a. Each Range L₁-L₂ is defined by two CNT filters represented by        a radius R₁ and R₂. Multiple ranges measured simultaneously can        be accommodated by feeding each range of a common manifold.    -   b. Each pair of CNT filters in a parallel analysis manifold can        be either:        -   i. Factory-installed        -   ii. Field depot-installed        -   iii. User-installed            2. Form factor can be understood in terms of current “smart”            cell phones.    -   a. Touch sensitive screen for both function set selection,        status readout, and output display.    -   b. Built in comm capability to enable receipt of local status of        forces information, weather models, adjacent detector warnings        with map location, and other advisory or backup data    -   c. Scrolling by page shifting touch    -   d. Magnification by two-finger motion or selection by one-finger        touch.    -   e. Backlit screen    -   f. Icons to reduce literacy requirement and provide language        transportability in combined military operations    -   g. Provision for downloading data to a central processor that        can be        -   i. Separately worn or carried by user        -   ii. Carried by other personnel        -   iii. Manned or Unmanned Ground, Sea or Air vehicle mounted        -   iv. At a base prior to leaving on mission    -   h. Battery recharging cable. Power sources can be in the above        locations (i-iv)    -   i. Incorporation of camera to send ancillary data to central        location for analysis to minimize need to record information on        surroundings.    -   j. GPS function handles all geolocation tasks    -   k. Target size and weight range of 3-16 oz.    -   l. Direct downloading of software to field unit for function        updating or to add field applications as wanted via a military        version of an “iTunes” store    -   m. Wireless, packet switching, anti-jam, and/or burst        communications        3. Additional Features/capabilities can be incorporated:    -   a. Field changes of battery    -   b. Clips and other attachment devices for user or vehicular use    -   c. Solar cell for battery recharging    -   d. Field or depot changeout of CNT filter pairs    -   e. Insertion of CNT sensors    -   f. Voice input/output        Examples of user modes include, e.g.,    -   a. Military missions where risk of attack must be considered.        This implies need for user stealth, small size, operation by        user in protective clothing    -   b. Field intelligence collection where size and weight        requirements can be relaxed, with suitable/flexible packaging    -   c. Environmental area survey    -   d. Incorporation of detector into a user local area net    -   e. Commercial chemical plant HAZMAT safety

4. Architectures

-   -   a. Detector architecture such as the U.S. Department of Defense        Common CBRN Sensor Interface (CCSI's specifications to allows        for families of compatible and interoperable devices) are        important    -   b. A communications architecture to fit the detector into an        existing or specified communications network    -   c. An information architecture to define data formats and with        interfaces to support two-way transmission of e.g., data,        software, warning, etc.    -   d. A logistics architecture to include        -   i. Device identification        -   ii. Device location        -   iii. Device user or organization association        -   iv. Calibration of detector        -   v. Status and maintenance condition        -   vi. Field diagnosis of malfunction        -   vii. Field repair such as resetting, recalibration,            switching to built-in redundant backup capability        -   viii. Logging past locations, past readings, malfunctions,            change in operator or organizational assignment        -   ix. Incorporation of ancillary sensing functions such as            temperature, humidity, impact, sound level, light level        -   x. Flexible growth of detector with time to incorporate new            or improved physical devices, software-defined new            functionalities, replacement of damaged components            5. Seamlessly incorporate the detector into systems planned            or extant of the Army, Air Force, Navy, intelligence            community and other user communities including but not            limited to the Environmental Protection Agency and other            environmental monitoring organizations; industry            associations such as water supply, industrial occupation and            industrial safety; Dept linent of Homeland Security,            particularly at state, county, and local levels; Federal            Emergency Management Agency (FEMA); Commercial Chemical            plant safety; education and training groups for university            level (teaching and laboratory safety) and training            (industrial, military, law enforcement, first responders,            disaster response, etc.); transportation security needs such            as passenger, baggage or freight inspector; incorporate            nuclear radiation sensor for border control to protect            against nuclear weapons and radiological threats; etc.

Inventive Example 1C

Another inventive example is as follows. Call the section between thefirst two valves, that contain two size filters L₁ and L₂ with a sensorin between a “cell” C₁₂. If P is the pump that draws the gas beingmeasured, then the detector can be denoted as -C₁₂-P-.

There are other physical configurations possible that lead to enhancedfunctionality. Suppose one wants to produce a continuous “spectrum” ofmolecular lengths: 1-2, 2-3, 3-4, . . . N-(N+1) between molecular length1 and length N+1. These would logically be in series, and denoted as:

-C ₁₂ C ₂₃ C ₃₄ . . . C _(N(N+1))-P-

Another useful geometry would meet the military need to classify adetected agent in a way that would assist in adopting appropriateprotective measures. For this there are three categories of agents ofcommon concern:

Blood agents: CK (cyanogen chloride; chemical formula CNCl) and AC(hydrogen cyanide; chemical formula HCN). These are quite small, of theorder of 0.4-0.5 nm. To detect them one must select that length range.

Another set of agents are the blister agents such as L (lewisite;chemical formula C₂H₂AsCl₃) are intermediate in length. Lewisite is 0.9nm while sulfur mustard (C₄H₈Cl₂S) is about 1 nm long. There are variousformulations of sulfur mustard, differing in being mixed with othermaterials to enhance its effects under various conditions.

In this case, therefore, one could make a sensor that distinguishesbetween the three classes, blood, blister, and nerve agents by selectingthree ranges: 0.4-0.5, 0.9-1.0. and 1.1-2.2 nm. In this case they wouldbe connected in parallel and each fed off a common manifold, and eachusing the same suction pump.

There can be combinations of serial and parallel cell arrangementschosen and fabricated to fit particular user needs. For example, sincethe size range of nerve agents is so large, one may want to divide itmore finely, breaking down the 1.1-2.2 nm range into a continuous lengthspectrum of four or five sub-pieces.

Another variation is to use either a second suction pump or the samesuction pump with a more complex set of valves and “piping” to feed anyof the contents of any of the concentration chambers between the CNTlength filters into a separate section C* based on other molecularparameters and using a sensor or sensors responsive to other physicalproperties such as dipole moment, chemical reactivity, etc. (C* may beconfigured in series and parallel, not shown.) This could be drawn as:

(For simplicity, without showing all valves).

The electronics may include other functions and be structured with anopen architecture to allow the device to become a subsystem of a largersystem or to provide a basis for adding on other subsystems to it.

Inventive Example 2 Operation of Flow Controller

A system 300 (FIG. 3) that receives air is constructed, comprising apump (P) to draw in air containing the analyte or analytes. The system300 further comprises at least one length separator 301 that selectsmolecules in a selected size range. The system 300 further comprises aconcentrator 311 integrated with each separator 301, whereinconcentrator 311 and length separator 301 may be the same component. Thesystem 300 further comprises a sensor (S) integrated with each separator301, the sensor (S) being a suitable sensor to detect the target analyteor analytes. The system 300 also comprises an analyzer 300A to interpretthe sensor outputs from each separator 301. The system 300 furthercomprises an interactive interrogator 305 which is acomputer-implemented system or device (such as, e.g., an interactiveinterrogator that receives at least one of: user inputs from a humanuser or users and/or receives data from a remote system and/or receivesor contains a library in a computer-readable form of analytes andpossible interferents). Also the system 300 comprises a flow controller(FC) to manage operation of the separator, concentrator 311, ambiguityresolver 303 if any, and to manage backwash operations includingoperation of the valves VEN, V11, V12, VN1, VN2, V3, V4, V5, VEX and thepump (P). The system 300 further comprises a vaporizer 302 to convertliquid-phase analytes in an airflow to vapor phase. Optionally thesystem 300 comprises an ambiguity resolver 303.

In FIGS. 3-4, N cells 33 are in parallel of which an example of a cell33 is shown in FIG. 3A.

Referring to FIG. 3, a pump (P) draws in a fluid to be sampled. The pump(P) has a volumetric capacity of R vol/sec. The system 300 comprises anentrance valve VEN and an exit valve VEX. Valves VEN and VEX areconnected to the flow controller (FC). By varying the size, weight, andpower consumption of the pump (P) used in system 300, the size, weight,power sensitivity, and measurement time of the system 300 can be varied.

Referring to FIGS. 3-4, one or more separators 33 are connected inparallel to an entrance manifold M1. In FIG. 4, the number of separators33 illustrated is merely representational of “N”, where N is an integer1 or greater. A separator 33 may also be referred to as a separator cell33.

A separator 33 has an entrance face which consists of an array ofroughly parallel nanotubes open at both ends and oriented in thedirection of the flow of the sampled fluid, each of roughly the sameinner diameter and roughly the same length, thus constituting a moleculefilter. The inner diameter D1 of each entrance face (i.e., the first)nanotube filter is equal to the minimum diameter of molecules to beexcluded from said separator 33. D1 is chosen to be slightly larger thanthat of the diameter of the analyte molecule or molecules. “Diameter ofthe molecule” means the maximum diameter swept out by a moleculerotating about an arbitrary axis through the center of mass of themolecule subject to normal thermal collisions before encountering thefirst nanotube filter.

The exit face of the separator 33 consists of an array of roughlyparallel nanotubes open at both ends and oriented in the direction ofthe flow of the sampled fluid, each of roughly the same inner diameterand roughly the same length thus constituting a second molecule filter.The inner diameter D2 of the exit face nanotubes are such that D2 equalsthe maximum diameter of the molecules not to be retained in saidseparator 33 but instead allowed to exit said separator 33.

The separator cell 33 (FIGS. 3-4) thus selects molecules whose maximumdiameter D falls within the range D1>D>D2. On one of the walls of thecell 33 is a sensor (S) that produces an electrical signal that is afunction of the concentration of the analyte molecule or molecules inthe sampled fluid drawn through by the pump (P). Such electricalconnections as required are passed through a wall of a chamber enclosingthe sensor (S), to the outside, and are available for connection to theanalyzer 300A.

A valve V11 at the entrance of the first separator cell of the separatorcells 33 and a valve V12 at the exit of the first separator cell of theseparator cells 33 is then closed by a flow controller (FC) when theanalyzer 300A determines that the analyte's or analytes' concentrationmeasurement is complete, or after a maximum pumping time set by theuser. When there is more than one separator cell 33, this step isperformed for each of the cells 33 at a time determined by the analyzer300A, or after a maximum pumping time set by the user.

In order for the fluid sample containing the analyte or analytes to beremoved from the cell 33 when commanded by the user at the conclusion ofthe measurement in preparation for a subsequent fluid sample to beintroduced into the cell, valves V11, V12 and VEN are opened, VEX isclosed, and the cell 33 is cleansed of the analyte or analytes throughback-flushing. Table 1 shows the position of each of the valves in thesystem 300 in the shut down state, during the measurement time, duringoperation of the ambiguity resolver 303, and during the backwashoperation.

TABLE 1 Ambiguity Resolution state Valves Shut-down Measurement(illustration Back-flush and Pump state operation for Cell 1 only)operation VEN closed open closed open V11 closed open closed open V12closed open open open VN1 closed open closed open VN2 closed open closedopen V3 closed open close open V4 closed closed open open V5 closedclosed open open VEX closed open closed closed Pump off on (inflow) on(inflow) on (outflow)For the system 300 in FIGS. 3-4, using at least one cell 33 (FIG. 3A),Table 1 shows whether each of valves VEN, V11, V12, VN1, VN2, V3, V4,V5, VEX is closed or open and whether the pump (P) is off or on fordifferent respective states and operations including a shut-down state,a measurement operation, an ambiguity resolution state and a back-flushoperation. In Table 1, the column for Ambiguity Resolution state is anillustration only for one cell 33.

Each separator cell 33 acts as a concentrator to increase thesensitivity of the system 300. For a separator cell 33 having a volumeV, the pump (P) will fill this volume V in a time T=V/R where R iscapacity of the pump (P). For a configuration having N cells 33 inparallel, each cell 33 the same size, the time to fill all of the cells33 is T=NV/R. Further suppose that the desired sensitivity of themeasurement of each cell 33 is a concentration of molecules of c/unitvolume but the maximum sensitivity of the sensor (S) is only smolecules/unit volume. It will be necessary to fill the cell 33 volumerepeatedly to achieve a concentration ratio CR that is s/c timesgreater, each time retaining the analyte or analytes until the cell 33volume has sufficiently concentrated the analyte or analytes such thatthe sensor (S) is able to register their presence. Therefore

TR=V×N×s/c

in which operational requirements of the system 300 will set T, c, andN. Therefore the pump capacity R is set by the cell volume V and themaximum sensitivity, s, of the sensor (S).

The sensor (S) in an integrated sensor/concentrator cell 33 operates inthe following manner. A sensor (S) has a resistance that is altered bythe attachment of an analyte molecule to a surface of the sensor (S) orto an internal structure of the sensor (S) forming one wall of theseparator/concentrator cell 33. At least two electrical connectionsincluding the two ends of a resistive element extend through a wall ofthe cell 33 and connect to the analyzer 300A.

The analyzer 300A consists of an electronic data processor. The analyzer300A comprises a voltage source that applies a voltage to each sensor(S). Each respective sensor (S) in each of the cells 33 need not beidentical in material or construction to another sensor (S). Theanalyzer 300A also has a voltage measuring capability that records thechange in resistance of the sensor (S) with exposure to the analyte oranalytes in the cell 33. The analyzer 300A comprises a clock thatprovides a time base against which to measure resistance changes andbased on which measurements and actions performed by the system 300 aretime-tagged. The analyzer 300A comprises an algorithm that recognizesresistance changes in the sensor (S) as a function of time, interpretsthis change in terms of chemical concentration, and determines aresponse of sensor (S) in accordance with procedures specified by theuser through the interactive interrogator 305. The analyzer 300Acomprises a display, such as a display that provides three coloredgreen/yellow/red lights viewable by a user for each of the respectivecells 33 in which green indicates that no analyte or analytes above auser-specified alerting threshold are present, yellow indicates thatsome analyte or analytes are present above a user-specified threshold,and red indicates that a user-specified dangerous level of analyte oranalytes is present. The analyzer 300A comprises a logic element thatgenerates required signals for the flow controller (FC) to open andclose valves. The analyzer 300A comprises logic elements based on whichthe system 300 provides more detailed information to the user through adisplay that is part of the interactive interrogator 305 and iscommanded by the user. The analyzer 300A comprises a logic element thatcommunicates such information as the user may have indicated to besupplied to a communications device for transmission to a higher levelsensor/response system of which system 300 is a subsystem or component.

The system 300 further comprises an interactive interrogator 305 whichreceives commands of a user. Interactive interrogator 305 providesenvironmental information to the user and analyzer 300A to determine aresponse, or range of responses, to be provided to the user through thedisplay. The interactive interrogator 305 may comprise, e.g., a receiverfor GPS coordinates; a communication capability for establishingconnection with a wind sensor; a digital camera; etc. Examples ofenvironmental information that the interactive interrogator 305 provides(such as providing in computer-readable form) to the analyzer 300A are,e.g., GPS coordinates of the sensor (S) at the time a measurement ismade; wind speed and direction (provided either by user measurement orestimate or from a wind sensor or database); environmental informationrelating to presence of possible chemical interferent sources needed bythe analyzer 300A to make correct deductions from measurements taken bysensor (S) and downloaded to the analyzer 300A (which environmentalinformation relating to presence of possible chemical interferentsources may be downloaded to the analyzer 300A from a remote database);a library of chemical compounds consisting of precursors or products(such as, e.g., a library of chemical compounds consisting of precursorsor products derived from actual activities observed by the user to bepresent); etc. In addition, a digital camera may optionally be used toproduce images, such as, e.g., images reviewable by a remote user at adifferent location away from the sensor (S) to evaluate the interferentpotential presented by the environment in the vicinity of the sensor(S).

In the system 300, the flow controller (FC) opens and closes valves,controls the flows into and out of the single or multiple cells 33,controls the operation of vaporizer 302, controls the flow to anoptional ambiguity resolver 303, and controls back-flush of the system300 following a measurement by sensor (S). The flow controller (FC)receives status information from the analyzer 300A when a cell 33 hascompleted a measurement, when the at least one cell 33 is to be emptiedin preparation for a next measurement sample, and when the user requestsinformation from the ambiguity resolver 303.

Under the temperature and pressure conditions when the measurement ormeasurements are made by the sensor (S), analytes can be in either avapor phase or can be small droplets of liquid phase. To be certain thatsuch analytes that are liquid droplets as may be present are completelymeasured, on entry into the system 300 they pass through a vaporizer 302that emits electrical, laser, thermal energy or other means sufficientto vaporize liquid phase analytes if any.

Inventive Example 2A Ambiguity Resolution

Referring to Example 2 and system 300, it is possible that uponcompletion of an analyte's or analytes' concentration measurement in acell 33, there maybe ambiguity as to whether the separated vapor is ananalyte or interferent. In such a case of a potential false positive,optionally the analyzer 300A communicates this status onwards, such as,e.g., communicating this status to the user for handling or the statusis directly presented by the flow controller (FC) to an ambiguityresolver 303. In the case in which the status is directly presented bythe flow controller (FC) to ambiguity resolver 303, the exit valve VN2on the cell or cells 33 that are registering are sequentially opened.Valve V3 is closed and valves V4 and V5 are opened and the concentratedsamples contained therein are presented to a follow-up sensor (not shownin FIGS. 3-4) which is not sensor (S), which follow-up sensor is capableof making a further determination based on a different physical propertyof the molecule or molecules than was sensed by sensor (S), withinformation relating to the different physical property being containedin the library.

This example a system 300 which includes a length separator 301 furtherincludes an ambiguity resolver 303 which is a hardware-based ambiguityresolver consisting of a sensor responsive to a physical characteristic(which is not a length characteristic) of an analyte or analytes.

Inventive Example 3 Reducing False Positives in Sensing Chemical WarfareAgents (CWA)

A preliminary spreadsheet was prepared for over 1700 compounds includingchemical warfare agents and the rest chemicals derived from an analysisof the list of DoD “interferents,” e.g. burning rubber and the chemicalcompounds derived from those processes. The DoD interferents areillustrative of combat operations and various chemicals such as arisingfrom vehicles and housekeeping materials typically found in closedspaces. Information such as chemical names, structural formula,molecular weight, melting point, boiling point (to know what are gasesat standard temperature and pressure), and vapor pressure was compiled.

Using molecular modeling software, maximum diameters of circumscribingspheres were calculated and tabulated.

From the preliminary spreadsheet, the false positive situation, namely,potential vapor phase false positives could be seen using molecularlength as the primary selection criterion. Based simply on molecularlength, there were 51 possible interferents.

Inventive Example 3A Ambiguity Resolution by Means of a Second PhysicalSensor

Although other alternative approaches for reducing the number of falsepositives in Example 3 may be possible, the preferred approach is to usea second selection criterion to rule out the possibility of a falsepositive. This has the advantage of not having to rely on localcircumstances, local judgments, and local expertise.

An example of a second selection criterion is molecular weight, such asby using in series with the CNT length selector, a mass spectrometer.

Table 2 is based on a length-first selection dividing the length rangein the preliminary spreadsheet from 0.63 nm to 1.39 nm into two ranges,0.63 to 0.97 nm and 1.04 nm to 1.39 nm. One then brackets the molecularweight of the chemical agents in each of these length ranges fromsmallest to largest and looks to see if any of the interferents stillfall into the joint selection range. The results for this example are:

TABLE 2 TOTAL NO. OF NO. OF NO. OF LENGTH LENGTHS LENGTH MOLECULARCHEMICAL INTERFERENTS INTERFERENTS RANGE SELECTED RANGE WEIGHT AGENTS ININ RANGE (LENGTH PLUS (NM) (NM) (NM) RANGE RANGE (LENGTH ONLY) MW) 10.63-0.97 0.34 140-180 5 32 2 2 1.04-1.39 0.35 198-239 5 19 0Examples 3-3A illustrate how to select detector parameters based on theproblem being addressed.

Upon applying the joint selection criteria of Examples 3-3A, only tworesidual interferents got through the joint selection criteria, 1,2dichlorobenzene and isopharone. Therefore through Examples 3-3A, thenumber of interferents has been substantially reduced from the beginningnumber.

Inventive Example 4B Application of Library of Analytes and Interferents

For constructing a table with rows that include at least one analyte andinclude interferents for that analyte, the following columns may beused: interferent source, chemical derived therefrom (from these twocolumns, a local user can indicate what is not present); molecularweight; melting point, boiling point (these columns are used to tellsolid from vapor from liquid); vapor pressure (possibly to rule out acompound); maximum diameter, of which the columns for interferent sourceand maximum diameter are considered most important.

In FIG. 2, the rows have been sorted by maximum diameter and are shownin increasing order of maximum diameter. Of the columns in FIG. 2,interferent source and maximum diameter are considered most useful fordesigning systems, methods, devices and apparatuses according to theinvention.

Inventive Example 5 Detecting Analytes in Water Samples

Referring to FIG. 7, the water being sampled is drawn continuously undersuction produced by pump P1 through the selector/concentrator cells S/C.For this to occur, valve VEN, V11 and V12 are open, as well as thecorresponding valves on the other selector/concentrator cells selectedfor use. In FIG. 7 only two S/C are shown for simplicity, S/C1 and S/C2so that V21 and V22 are open also.

The water flow (FIG. 7) continues as with the air sampling case. Eachselector/concentrator cell has two molecular-length defining pairs ofCNT filters, one at the entrance and one at the exit of the cell asshown in FIG. 1. In this way molecules of a specified size range arecaptured and retained.

The sampled water first enters manifold M1 (FIG. 7) from which it flowsto the active selector/concentrator cells and the outflow from each ofthe selector/concentrator cells is collected in manifold M2 prior toexiting the apparatus through valve VEX which is open. The only featuredifferent from the air case is that bodies of water will have a varietyof types and sizes of particulate matter. These must be excluded lestthey clog the CNT filters and so a conventional particulate filter isshown after entrance valve VEN and before manifold M1 (FIG. 7). The poresize of this conventional filter is chosen based on the size of theparticulates present in the sampled water. Typically it will be of theorder of 1 micron.

Valves V13 and V14 (FIG. 7) are closed, as well as the correspondingvalves for S/C2 which is similarly constructed but with CNT filtersselected to be of a size that a different desired molecular length rangeis defined. In FIG. 7 as shown in FIG. 4 there is no limit to the numberof selector/concentrator cells that may be operated in parallel beyondthe ultimate practical limits on size, cost, and power.

As with air sampling, pump P1 (FIG. 7) is operated for a time set by theuser, that time being selected to increase the sensitivity of theapparatus such that it will be able to register toxic materials atlevels deemed harmful.

When the pumping time has been reached, pump P1 is closed down as wellas valves V11 and V21 (in this example of two selector/concentratorcells in use.) The apparatus is now filled with water in what might becalled the “water loop.” The water in the selector/concentrator cellscontain, in addition, concentrated analytes whose molecular size fallswithin the CNT filter-defined length ranges. All other parts of theapparatus are dry. At this point the analytes have not been presented toa sensor and thus have registered no signal, for the reason that nosuitable sensors capable of operating in an aqueous environment areavailable.

The next step is to drain out the water from the selector/concentratorcells. This is done by restarting the pump P1 and opening valves V13 andV23. This allows the water to be pulled out of the water loop of theapparatus and replaced by air that flows into each activeselector/concentrator cell through manifold M3. When this is completed,V12 and V13, are closed and valve V14 is opened, valve V15 remainingclosed, and the corresponding valves on S/C2 operated similarly. Thisresults in the air enriched with analytes extracted from the watersample in S/C1 being exposed to sensor S1, and similarly for S2. Becausethe partial pressure of the analytes in S/C1 is greater than that in S1,which is devoid of analytes, mixing will occur and S1 (FIG. 7) will beable to respond with the same kind of electrical signal as in the caseof the air sampled flow in FIG. 4. The speed of this mixing could beincreased by heating S/C1 to increase the pressure of the gases thereinshould this be deemed important for a particular sampling application.This part of the apparatus can be called the “air loop.”

When the measurement of the analyte concentrations in theselector/concentrator cells is completed, the apparatus must be clearedto prepare it for the next water sample. This sample could be in adifferent field location, or the same location at some later time, orfor a next sample to be measured in a central measurement laboratoryundertaking this kind of analysis as an internal service or as acommercial service.

At this point there are two ways of proceeding. If the measurement isdeemed to be unambiguous, valves V13, V15, V3, and VEX are opened, withV4 and V5 remaining closed, and pump P2 pulls the air into manifold M4and out of the apparatus and the subsequent flow cleans all the analytein S/C1 and S1 from the air loop. This process is repeated sequentiallyfor all the other selector/concentrator cells employed.

If, however, there is an ambiguity in the measurement from S1, V3 isclosed and valves V4 and V5 opened and pump P2 presents the ambiguitysensor with the analyte or analytes from S1. This process is repeatedfor all the other selector/concentrator cells employed requiringambiguity resolution.

In addition to back-flushing the air loop, the water loop must beback-flushed. This is done by opening VEN, V11, V12, and thecorresponding valves on S/C2 and all other active selector/concentratorcells. Pump P1 is then reversed and it pushes sample water through thewater loop. The CNT filters do not impede the cleaning of eachselector/concentrator cell since the analyte molecules can flow backthrough the CNT filters past which they entered.

At this point all valves are returned to their initial position and theapparatus is ready for the next sample.

The following Table 2 summarizes the valve positions and pump operationfor the several states of the apparatus. The information is, forsimplicity, shown for the case of only one active selector concentratordell, S/C1:

TABLE 2 MOVE VALVES DRAIN ANALYTES TO AND SHUT-DOWN WATER SEL/CONC AIRLOOP AMBIGUITY BACK-FLUSH BACK-FLUSH PUMPS STATE SAMPLING CELL SENSORRESOLUTION AIR LOOP WATER LOOP VEN closed open closed closed closedclosed open V11 closed open closed closed closed closed open V12 closedopen open closed closed closed open VI3 closed closed open open closedopen closed V14 closed closed closed open closed closed closed V15closed closed closed closed open open closed V3 closed closed closedopen closed open closed V4 closed closed closed closed open open closedV5 closed closed closed closed open open closed VEX closed closed closedclosed closed open closed P1 off on(suction) on(suction) on(suction) offoff on(pressure) P2 off off off off on(suction) on(suction) off

While the invention has been described in terms of a preferredembodiment, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1-3. (canceled)
 4. The method of claim 11, comprising: screening theinitial sample to produce a screened sample consisting of molecules ofsize smaller than a maximum size; and requiring molecules of sizesmaller than a minimum size to exit.
 5. The method of claim 4,comprising producing a target sample consisting of molecules having asize in the predefined size range.
 6. The method of claim 4, wherein thestep of screening the initial sample to produce a screened sampleconsisting of molecules of size smaller than the maximum size includesapplying a screen comprising at least one nanotube having an innerdiameter to exclude molecules bigger than the maximum size.
 7. Themethod of claim 4, wherein the step of requiring molecules of sizegreater than the minimum size to exit includes applying a screencomprising at least one nanotube having an inner diameter that permitspassage of molecules below the minimum size.
 8. The method of claim 4,comprising passing the initial sample through a screen comprising atleast one nanotube having an inner diameter to exclude molecules biggerthan the maximum size, followed by withdrawing, through a screencomprising at least one nanotube having an inner diameter that permitspassage of molecules below the minimum size, a subset of molecules whichare smaller than the minimum size.
 9. The method of claim 4, comprisinga screening step of screening an initial sample comprising at least oneof an analyte molecule and/or a molecule that evokes a false positivefor the analyte molecule.
 10. The method of claim 4, comprising ascreening step of screening an initial sample comprising at least one ofan analyte molecule and/or a molecule that evokes a false positive forthe analyte molecule and is of a different size than the analytemolecule.
 11. A method of reducing or avoiding false alarms by a sensortuned to a target molecule that is sarin or VX, comprising: receivinginto a container an initial sample that contains various-sizedmolecules, followed by reducing the initial sample to a subset ofmolecules of a predefined size range; bringing only the subset ofmolecules of the predefined size range into contact with the sensor. 12.The method of claim 11, wherein the initial sample includes at least oneof an analyte molecule and/or a molecule that evokes a false positivefor the analyte molecule.
 13. (canceled)
 14. The method of claim 11,wherein the initial sample includes a set of molecules that are of arelatively large size, a set of molecules that are of a relatively smallsize, and target set of molecules that are of a medium size which is thepredefined size range, and the reducing step reduces the initial sampleto the target set.
 15. The method of claim 11, wherein the reducing stepcomprises screening-out too-big molecules and further comprises a stepof requiring too-small molecules to exit while screening-in target-sizemolecules.
 16. The method of claim 11, wherein the reducing step sortsat least one molecule that would evoke a false positive and prevents themolecule that would evoke the false positive from coming in contact withthe sensor.
 17. A method of removing, from an initial sample, a subsetof molecules that would activate false positives by a sensor which isintended to detect a molecule or molecules wherein the analyte moleculeor molecules have an identified size range, comprising: removing fromthe initial sample molecules outside the identified size range of theanalyte molecule or molecules.
 18. The method of claim 17, wherein theremoving step comprises applying at least a first screen comprising atleast one nanotube of an inner diameter that excludes too-big molecules,and further comprises requiring too-small molecules to exit through atleast one nanotube of an inner diameter that permits passage oftoo-small molecules.
 19. (canceled)
 20. A method of processing aninitial sample of a set of molecules before contact with a sensor,comprising: directing the initial sample into contact with an entryscreen leading into a container, the entry screen excluding from entry asubset of molecules bigger than a molecules size range of moleculeswanted to be detected by the sensor; withdrawing from the container asubset of molecules smaller than the molecular size range of moleculeswanted to be detected by the sensor.
 21. The method of claim 20, whereinthe initial sample includes at least one molecule that would evoke afalse-positive if presented to the sensor and after the directing stepand the withdrawing step, the molecule that would evoke a false positiveis not within the container. 22-25. (canceled)
 26. The method of claim11, comprising: screening from entry into the container molecules whichare bigger than the target molecule to which the sensor is tuned;withdrawing from the container molecules which are smaller than thetarget molecule to which the sensor is tuned, until the container onlycontains molecules of a size of the target molecule, to be sensed by thesensor; and after the screening and withdrawing steps, operating thesensor.
 27. The method of claim 26, wherein the screening step comprisesproviding a screen that comprises nanotubes.
 28. The method of claim 26,wherein the withdrawing step comprises withdrawing molecules throughnanotubes.
 29. The method of claim 11, comprising operating a flowcontroller.